1. Field of the Invention
The present invention relates to a liquid-discharging head that discharges a liquid and a method of producing the same. More specifically, the present invention relates to an ink-jet recording head that performs recording by discharging ink onto a recording medium, and a method of producing the same.
2. Description of the Related Art
A liquid-discharging head, such as an ink-jet head, includes discharge ports, liquid passages communicating with the discharge ports, energy-generating units for discharging a liquid, the units being disposed in the liquid passages, a liquid chamber communicating with the liquid passages, and a supply port for supplying ink from an ink tank or the like to the liquid chamber. Ink droplets are discharged from the discharge ports by providing energy generated by the energy-generating units to the ink filling the liquid passages. These discharged ink droplets land on a recording material to form pixels, and thus recording is performed.
Among these liquid-discharging heads, liquid-discharging heads that utilize thermal energy for discharging a liquid can perform recording with a high resolution because a plurality of discharging ports can be arranged in a high density. Furthermore, such liquid-discharging heads are advantageous in that the size of the heads can be easily reduced as a whole.
In general, in such a known liquid-discharging head that utilizes thermal energy, a high-density arrangement is realized by arranging a plurality of exothermic resistive elements in line on a substrate made of, for example, silicon, and a substrate having a heat storage layer and an electrical insulating layer that are used in common for the plurality of exothermic resistive elements is used.
U.S. Pat. No. 6,984,024 discloses a back-shooting-type head, which is an example of an ink-jet head. In a thermally driven ink-jet head, air bubbles are formed in ink by heat generated by an exothermic resistive element (heater) disposed in a liquid passage, and the ink in the liquid passage is discharged from a discharge port by the pressure generated by the growth of the air bubbles. An ink-droplet discharge system in which an ink droplet is discharged in a direction opposite to the direction in which a heater surface on which the air bubbles expand faces is referred to as “back-shooting type”.
The back-shooting type head described in U.S. Pat. No. 6,984,024 is produced using a silicon-on-insulator (SOI) wafer. For example, a silicon surface layer and an insulating layer that constitute the SOI wafer have a thickness of 40 μm and 1 μm, respectively. In a production process of the head, first, an ink chamber and a wall of an ink channel are formed. More specifically, a trench is formed, and the trench is then embedded by thermal oxidization. The oxidizing film functions as a stop layer of final isotropic etching using XeF2. After the thermal oxidization, the thermally oxidized film formed on the surface of the substrate is removed by chemical mechanical polishing (CMP).
Subsequently, a heater lower layer, a heater layer and a wiring layer (heater upper layer), and a metal protective film are formed and patterned. Next, a metal seed layer for electroplating is formed, and a positive resist used as a pattern of discharge ports is patterned. A nickel film is formed as a discharge port plate by electroforming so as to have a thickness of 30 μm. Subsequently, a manifold is formed by etching silicon of the lower layer, the insulating layer is then etched. Parylene is then deposited in order to protect exposed silicon portions. Subsequently, a part of the parylene disposed parallel to the substrate surface is etched in order to remove silicon located on positions corresponding to the discharge ports. Finally, the ink chamber and the ink channel communicate with the discharge ports by performing isotropic etching with XeF2.
Nowadays, a large number of recording apparatuses are used, and, for example, high-speed recording, high resolution, high image quality, and low noise have been required for these recording apparatuses. An example of a recording head of a recording apparatus that meets such requirements is an ink-jet head. In an ink-jet head that discharges ink by utilizing thermal energy, stabilization of ink discharge, i.e., stabilization of the amount of ink discharge required for meeting the above needs are significantly affected by the temperature of ink in discharge portions. Specifically, if the temperature of the ink is excessively low, the viscosity of the ink excessively increases. As a result, the ink cannot be discharged by normal thermal energy. On the other hand, if the temperature is excessively high, the amount of discharge increases, and for example, ink may be spilled onto a recording sheet, resulting in a degradation of image quality. Furthermore, in order to realize high-speed recording, a drive frequency (drive frequency for which the time ranging from a discharge of a droplet to the next discharge is defined as one cycle) must be increased by efficiently dissipating heat generated from a heater without storing the heat in a substrate.
On the other hand, in a back-shooting-type ink-jet head, heaters are provided in a discharge port plate having a thickness of about 30 μm. In this structure, the temperature of ink is easily increased because portions having the heaters have a low heat capacity, as compared with a head in which a discharge port plate including liquid passages having heaters therein is stacked on a silicon substrate on which the heaters are formed. Therefore, such a back-shooting-type head is disadvantageous in that the temperature of ink is easily increased, and it is difficult to stabilize the amount of discharge.